This invention relates to digital switching network and, more particularly, to multi-line telephone systems providing an interface between large key telephones and a multiplicity of analog and digital lines.
Multi-line telephone key stations, sometimes referred to as "trader turrets", are widely used in rapid communication networks such as trading operations in banks, brokerage houses, and other financial institutions. Telephones of this type provide direct access to a large number of telephone lines with a line being selected by the depression of a single key on the key station. A large trading room can include many telephone key stations for simultaneously completing many transactions each involving many millions of dollars. Trader turrets generally include at least thirty line keys and often have several hundred. Trader turrets are normally used in networks where the number of lines is greater than the number of telephones whereas, with normal telephone key stations, the number of telephones exceeds the number of lines.
Each telephone key station may have access to other telephone key stations in the system within a trading room and to a large number of outside lines and private lines. Each telephone user may be connected to several lines or terminals at the same time in a conferencing mode.
A typical trading transaction involves a rapid series of short telephone conversations to, for example, locate traders having the desired security for sale at the best price. A typical call lasts a few seconds and there may be many calls per minute during the course of a single transaction. It is important for a trader to have immediate access to outside lines irrespective of system load conditions.
System-wide failures cannot be tolerated, since such failures, even short ones, if they occur at peak trading times can result in huge losses of business. In addition, as demand for additional capacity increases, there is need for a system which can be expanded as desired without system down time. Examples of a prior continually expandable telephone switching networks intended for general systems use are disclosed in U.S. Pat. No. 4,173,713, issued to Giesken et al. and U.S. Pat. No. 4,201,891, issued to Lawrence et. al.
To avoid system-wide failures, a distributed architecture is essential so that there will be no single point failure that can cause a catastrophic system-wide failure. A distributed architecture for a traditional network is shown in U.S. Pat. No. Re. 31,144 issued to Feil. Other examples of distributed control of digital switching networks are disclosed in U.S. Pat. No. 4,201,889 issued to Lawrence et al., U.S. Pat. No. 4,317,962 issued to Cox et al. and U.S. Pat. No. 4,998,275 issued to Braunstein et. al. The technology disclosed in the later group of patents provide for a digital switching network with limited distributed processing for controlling a telephone digital switching network.
A major problem with implementing highly distributed processing systems with multiple processors is maintaining effective communication among the processors. In prior systems, in order to communicate with other processors in the system, each processor had to know the system architecture including specifically the code name, location, assigned tasks, and data format of other processors in the system. Therefore in a digital switching environment a sending processor had to know where the destination processor was physically located in the system and set a route through the network based on that overall knowledge of the system's topology. This approach tends to make the system rigid and inflexible to system changes. Furthermore, such systems where routing is based on known architecture tend to have relatively inflexible routing which does not effectively find routes around faults in the system.